As a representative example of this kind of coil composite molded body, there is a reactor which is an inductance part.
In hybrid vehicles, fuel cell vehicles, electric vehicles, or the like, a booster circuit is provided between a battery and an inverter which supplies alternating current power to a motor (electric motor), and a reactor (choke coil) which is an inductance part is used in the booster circuit.
For example, in hybrid vehicles, a maximum voltage of the battery is approximately 300 V. On the other hand, it is necessary to apply a high voltage of approximately 600 V to the motor so as to obtain large output. Therefore, a reactor is used as a part for the booster circuit.
A reactor is widely used for the booster circuit in photovoltaic power generation, or the like.
Conventionally, as the reactor, there has been generally used one in which an electric coil (hereinafter, the electric coil may be simply referred to as a “coil”) is wound around the periphery of a core which is configured so that a pair of U-shaped core pieces is disposed in a state where a predetermined gap is generated between end surfaces of each of the core pieces.
However, in the case of this type of reactor, since the coil is exposed to the outside, there are problems in that coil vibration occurs according to excitation of the coil, the vibration becomes noise, a size of the gap between the coil pieces should be determined with high accuracy, an assembly process between the core and the coil is needed, and the like. Therefore, there has been proposed a reactor in which a core is configured of a molded body (soft magnetic resin molded body) including a mixture of a soft magnetic powder and a resin and the coil is integrally included in a state of being embedded in the inner portion of the core.
For example, Patent literature 1 and Patent literature 2 below disclose this type of reactor and a method of manufacturing the same.
In methods of manufacturing the reactor described in Patent literature 1 and Patent literature 2, a mixture, in which soft magnetic powder is mixed so as to be a dispersion state in liquid of a thermosetting resin, is injected into the inner portion of an outer case or a container in a state where a coil is set to the inner portion of the outer case or the container, and thereafter, this is heated to a predetermined temperature and the resin liquid is subjected to a hardening reaction for a predetermined time, so that a core is integrated with the coil at the same time when the core is molded.
In the case of the reactor which is obtained in this way, there are advantages that occurrence of noise due to the coil vibration can be prevented, setting the gap between the core piece and the core piece with high accuracy is not needed (a minute gap is formed between the soft magnetic powders of the molded body core), the assembly process between the core and the coil is not needed, the coil can be protected from the outside by the core (soft magnetic resin molded body), and the like.
However, in this case where the liquid of the thermosetting resin in which the soft magnetic powder is mixed in a dispersion state is injected into the container in the state where the coil is set into the container, as shown in a schematic view of FIG. 10, the soft magnetic powder 14 (hard metal iron powder or the like is used as the soft magnetic powder 14) strongly strikes an insulating coating 12 on a surface of a wire 11 of the coil 10 or scratching occurs (in the case of the core of the reactor, generally, approximately 50 to 70% in terms of volume % of the soft magnetic powder such as the iron powder is contained) due to the injection pressure or the flow pressure at the time of the injection, and whereby, there occurs a problem that damage such as tearing of the insulating coating 12 on the surface of the coil 10 occurs.
In general, a coil with attached insulating coating is used as the coil 10, in which a wire 11 in which the insulating coating 12 has been attached and formed on the outer surface thereof in advance is wound. Generally, a liquid (varnish) having a predetermined viscosity, which is formed by dissolving an insulating resin (for example, polyimide-imide) in a solvent, is coated on the entire outer surface of the wire 11 which forms the coil 10, and thereafter, the coated wire is subjected to a drying and a hardening reaction for film formation, whereby the insulating coating 12 is obtained. However, the film thickness of the insulating coating 12 is thin at approximately 25 μm, and the insulating coating 12 may be damaged if the soft magnetic powder 14 such as iron powder strongly strikes the insulating coating 12 or scratching occurs at the time of molding the core.
If the insulating coating 12 is damaged in this way, insulating performance of the coil 10 is decreased, and voltage resistance (resistance to dielectric breakdown voltage) characteristics in the reactor are decreased.
In addition, when the coil is set into the container and the mixture of the soft magnetic powder and the liquid of the thermosetting resin is injected, there occurs a problem that the coil is deformed due to the injection pressure or the flow pressure.
The coil itself is simply deformed by elongation like an accordion or is easily deformed by twisting, and when the mixture of the soft magnetic powder and the liquid of the thermosetting resin is injected into the container, the coil is easily deformed due to the injection pressure or the flow pressure.
If the coil is deformed in this way, the performance as the reactor is deteriorated.
In addition, there occurs a problem that stress is added to the insulating coating due to hardening shrinkage when the thermosetting resin is hardened, and the insulating coating is damaged by the stress also at that time.
Moreover, as another method of manufacturing the reactor, a method is considered in which the coil is set into a cavity of a molding die and the mixture of the soft magnetic powder and a thermoplastic resin are injected into the cavity, so that the core is whereby injection-molded and also the coil is integrated in a state of being embedded in the inner portion of the core.
Particularly, when the core is molded by means of the injection-molding, there occurs a problem that, since the coil is easily deformed due to a strong injection pressure and flow pressure and the soft magnetic powder strongly strikes the insulating coating 12 of the coil or the scratching occurs, the insulating coating is more easily damaged.
In addition, particularly, when the core is molded by means of the injection-molding, there occurs a difficult problem that a thermal stress is added to the insulating coating due to expansion through the beating and shrinkage through cooling at the time of molding, and the insulating coating is thus damaged due to the thermal stress.
For example, the temperature of the thermoplastic resin that includes the soft magnetic powder at the time of the injection into the cavity of the molding die is 300° C. or more in a liquid of a molten state, and after the injection, it is cooled through the molding die and solidified, and becomes a molded body.
At this time or thereafter, in the process in which the molded body is taken out from the molding die and is cooled to room temperature, the core which is the molded body is largely shrunk. Accordingly, great stress acts on the insulating coating of the coil due to difference of shrinkage amount between the core and the coil when the core is shrunk, and thus, distortion occurs on the insulating coating, and the insulating coating is broken or damaged due to the distortion, or the like.
This also adversely affects the voltage resistance characteristics of the reactor.
In addition, as described above, since the film thickness of the insulating coating on the wire surface in the coil is originally thin, there is a problem in that reliability of the voltage resistance characteristics is not sufficient.
The above case is the case where the coil with attached insulating coating is used. However, even when the coil with attached insulating coating is not used, and a coil in which the wire is configured to be wound in a state where an insulating layer is interposed between uncoated wires is used, there are problems that the coil is deformed at the time of molding a core, the reliability of the voltage resistance characteristics is not sufficient, and the like, which are similar to the case where the coil with attached insulating coating is used.
Therefore, as measures against the above-described problems, it is considered that the coil may be encased in a state of being enclosed with an electrically insulating resin so that the coil becomes an encased coil body in advance, and in this state, the core is molded in a state where this is integrally included in the core.
Conventionally, for example, Patent literature 1 and Patent literature 3 below describe that the coil is made into such an encased coil body,
However, as the method of molding the encased coil body, specifically, as the method of manufacturing the resin covering layer, a method in which a thermoplastic resin is used and the resin is injection-molded is a suitable method because the molding can be performed in a short time and productivity is high. However, even in this case, how to hold the coil in the state of being positioned in the cavity of the molding die and how to prevent the deformation of the coil due to the injection pressure or the flow pressure become great problems.
If the coil is largely deformed at the time of molding, characteristics of the reactor deteriorate similarly as described above.
Problems of the encased coil body used in a reactor are described above with taking the reactor as an example,. However, the problems may similarly occur also in an encased coil body which is used in a coil composite molded body, other than the reactor.